This invention relates to multi anvil devices and, more particularly, to cubic multi anvil devices.
Devices for generating high pressure and high temperature conditions have been developed in the prior art to meet research and industrial needs. Geophysical and petrological research require apparatuses which are capable of simulating sub-surface conditions of the Earth, including simultaneously generated high pressure and high temperature conditions. Likewise, industrial production of diamonds also requires apparatuses capable of simultaneously generating high pressure and high temperature conditions. To this end, various multi anvil apparatuses have been developed in the prior art which are capable of generating substantially hydrostatic pressure conditions on a sample, while heating the sample. The apparatuses typically consist of variously shaped cooperating members assembled to receive externally applied forces, such as from a hydraulic press or a pressure ram, and convert the forces to substantially hydrostatic pressure acting on a centrally located polyhedral sample vessel, which accommodates the sample. Sample vessels have been formed with many shapes including cubic, tetrahedral and octahedral. In all of the prior art apparatuses, the cooperating members of the devices are formed to engage each face of the sample vessel in face-to-face engagement and press thereupon, such that the cumulative affect of pressing all the faces of the sample vessel results in volume reduction of the sample vessel and pressure being applied to the sample enclosed within the vessel. Pressure conditions at the sample vessel are substantially hydrostatic with the pressure acting on each face of the sample vessel being substantially equal as if the pressure was generated under hydrostatic conditions, rather than solid state.
Since volume reduction of the sample vessel is desired, the sample vessel must be formed from a deformable material. Under pressure applied by a multi anvil device, the sample vessel will deform with the material making up the sample vessel being extruded into clearances defined between the pressure-applying members of the device. Limited extrusion of the sample vessel material is desired to achieve two purposes. First, the extruded material acts as gaskets about the sample vessel which limit the amount of sample vessel material which is actually extruded. As pressure is applied to the sample vessel, increasing amounts of the material are extruded until the shear strength of the material resists further extrusion. Material with insufficient shear strength will not provide the gasket functions described above. If excessive material is extruded between the pressure-applying members, the extruded material will absorb the pressure exerted by the pressure-applying members, and little or no pressure will be applied to the sample vessel. Consequently, no work is performed on the sample vessel.
A second function of the extruded material is to provide massive support for the members applying pressure to the sample vessel. Typically, tungsten carbide is used in forming the pressure-applying members which press against the sample vessel. Many prior art apparatuses generate pressure conditions at the pressure-applying members which are greatly in excess of the compressive strength of tungsten carbide. The extruded sample vessel material acts as supportive gaskets between the various tungsten carbide pressure-applying members. With prior art apparatuses which operate above the compressive strength of tungsten carbide, the extruded sample vessel material provides support about the pressure-applying members which prevents the tungsten carbide from failing during operation.
Castable ceramics have been used in the prior art to form sample vessels, including MgO based materials, Al.sub.2 O.sub.3 based materials, SiO.sub.2 based materials, and Zircon-MgO (zirconia) based materials. Prior art sample vessels have been formed with peripherally extending gaskets, which resemble fins, and which are disposed in between the pressure-applying members. Frictional forces are generated between the fins and the pressure-applying members which limit the extrusion of the sample vessel materials to amounts less than that which is extruded with a comparable "finless" design.
Prior art cubic multi anvil devices suffer from several drawbacks. First, the apparatuses are formed with two spaced one-piece end plates which each have planar outer surfaces in face-to-face engagement with components of the external pressure source. The inner face of each of the end plates is configured with various inwardly extending, angled surfaces which are intended to angularly engage individual pressure receiving members disposed between the end plates and urge the pressure receiving members inwardly to apply pressure horizontally on the sample vessel. Simultaneously, the end plates directly apply pressure to the opposing vertical faces of the cubic sample vessel, and, consequently, pressure is applied to all six faces of the cubic sample vessel. The unitary construction of the end plates, however, is susceptible to high stress concentrations at central portions thereof due to the combined effect of directly transmitting pressure to the respective vertical face of the cubic sample vessel and urging the pressure receiving members horizontally inwardly towards the cubic sample vessel. The high stress concentrations prevent prior art apparatuses from achieving higher working pressures. A second drawback of the prior art apparatuses is the accommodation of limited volumes of sample material. Typical prior art apparatuses are able to accommodate sample volumes on the order of tens of cubic millimeters. However, research institutions and commercial facilities require the accommodation of larger samples.
It is an object of the subject invention to provide a multi anvil device for use with a cubic sample vessel which overcomes the shortcomings of the prior art.
It is also an object of the subject invention to provide a zirconia cubic sample vessel with lanthanum chromite disposed therein for reaction to an electrical flow and the heating of an enclosed sample material.
It is a further object of the subject invention to provide a multi anvil device comprised of unconstrained pressing members.
It is yet another object of the subject invention to provide a multi anvil device encompassed by an axially unconstrained locking ring which is reactive to the misalignment of forces applied to the multi anvil device.
It is still yet another object of the subject invention to provide a multi anvil device formed with a plurality of cooperating members which collectively define a right cylindrical form with a central hollow cuboidal space for accommodation of a cubic sample vessel.